Keysight X-Series Signal Analyzer This manual provides documentation for the following Analyzers: N9040B UXA N9030B PXA N9020B MXA N9010B EXA N9000B CXA N9063C Analog Demod Measurement Application Measurement Guide
Notices Keysight Technologies, Inc. 2008-2016 No part of this manual may be reproduced in any form or by any means (including electronic storage and retrieval or translation into a foreign language) without prior agreement and written consent from Keysight Technologies, Inc. as governed by United States and international copyright laws. Trademark Acknowledgments Manual Part Number N9063-90001 Edition Edition 1, February 2016 Supersedes: June 2015 Printed in USA/Malaysia Published by: Keysight Technologies 1400 Fountaingrove Parkway Santa Rosa, CA 95403 Warranty THE MATERIAL CONTAINED IN THIS DOCUMENT IS PROVIDED AS IS, AND IS SUBJECT TO BEING CHANGED, WITHOUT NOTICE, IN FUTURE EDITIONS. FURTHER, TO THE MAXIMUM EXTENT PERMITTED BY APPLICABLE LAW, KEYSIGHT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED WITH REGARD TO THIS MANUAL AND ANY INFORMATION CONTAINED HEREIN, INCLUDING BUT NOT LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. KEYSIGHT SHALL NOT BE LIABLE FOR ERRORS OR FOR INCIDENTAL OR CONSEQUENTIAL DAMAGES IN CONNECTION WITH THE FURNISHING, USE, OR PERFORMANCE OF THIS DOCUMENT OR ANY INFORMATION CONTAINED HEREIN. SHOULD KEYSIGHT AND THE USER HAVE A SEPARATE WRITTEN AGREEMENT WITH WARRANTY TERMS COVERING THE MATERIAL IN THIS DOCUMENT THAT CONFLICT WITH THESE TERMS, THE WARRANTY TERMS IN THE SEPARATE AGREEMENT WILL CONTROL. Technology Licenses The hardware and/or software described in this document are furnished under a license and may be used or copied only in accordance with the terms of such license. U.S. Government Rights The Software is commercial computer software, as defined by Federal Acquisition Regulation ( FAR ) 2.101. Pursuant to FAR 12.212 and 27.405-3 and Department of Defense FAR Supplement ( DFARS ) 227.7202, the U.S. government acquires commercial computer software under the same terms by which the software is customarily provided to the public. Accordingly, Keysight provides the Software to U.S. government customers under its standard commercial license, which is embodied in its End User License Agreement (EULA), a copy of which can be found at http://www.keysight.com/find/sweula The license set forth in the EULA represents the exclusive authority by which the U.S. government may use, modify, distribute, or disclose the Software. The EULA and the license set forth therein, does not require or permit, among other things, that Keysight: (1) Furnish technical information related to commercial computer software or commercial computer software documentation that is not customarily provided to the public; or (2) Relinquish to, or otherwise provide, the government rights in excess of these rights customarily provided to the public to use, modify, reproduce, release, perform, display, or disclose commercial computer software or commercial computer software documentation. No additional government requirements beyond those set forth in the EULA shall apply, except to the extent that those terms, rights, or licenses are explicitly required from all providers of commercial computer software pursuant to the FAR and the DFARS and are set forth specifically in writing elsewhere in the EULA. Keysight shall be under no obligation to update, revise or otherwise modify the Software. With respect to any technical data as defined by FAR 2.101, pursuant to FAR 12.211 and 27.404.2 and DFARS 227.7102, the U.S. government acquires no greater than Limited Rights as defined in FAR 27.401 or DFAR 227.7103-5 (c), as applicable in any technical data. Safety Notices A CAUTION notice denotes a hazard. It calls attention to an operating procedure, practice, or the like that, if not correctly performed or adhered to, could result in damage to the product or loss of important data. Do not proceed beyond a CAUTION notice until the indicated conditions are fully understood and met. A WARNING notice denotes a hazard. It calls attention to an operating procedure, practice, or the like that, if not correctly performed or adhered to, could result in personal injury or death. Do not proceed beyond a WARNING notice until the indicated conditions are fully understood and met.
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Contents Table of Contents 1. Demodulating AM, FM, ΦM, FM Stereo/RDS Signals Setting Up and Making a Measurement.......................................... 8 Making the Initial Signal Connection.......................................... 8 Using Analyzer Mode and Measurement Presets................................ 8 Demodulating an AM Signal................................................... 9 Demodulating an FM Signal.................................................. 11 Demodulating an FM Stereo/RDS Signal........................................ 13 Measuring L Only FM Stereo/RDS Signals.................................... 13 Measuring L=R FM Stereo/RDS Signals...................................... 19 2. Concepts AM Concepts.............................................................. 26 FM Concepts............................................................... 28 FM Stereo/RDS Concepts.................................................... 30 FM Stereo.............................................................. 30 RDS/RBDS............................................................. 30 Modulation Distortion Measurement Concepts.................................... 32 Purpose................................................................ 32 Measurement Technique.................................................. 32 Modulation SINAD Measurement Concepts...................................... 33 Purpose................................................................ 33 Measurement Technique.................................................. 33 N9063C Analog Demod Measurement Guide 5
Contents 6 Keysight N9063C Analog Demod Measurement Guide
Keysight X-Series Signal Analyzer N9063C Analog Demod Measurement Application Measurement Guide 1 Demodulating AM, FM, ΦM, FM Stereo/RDS Signals The Analog Demod measurement application provides the capability of demodulating AM (amplitude modulated), FM (frequency modulated), ΦM (phase modulated), and FM Stereo/RDS (Radio Data System) signals. These measurements provide functionalities that can generally be categorized as follows: Demodulating a modulated carrier and playing the modulating signal over a speaker (sometimes referred to as tune and listen) Displaying demodulated signals in both time and frequency domains Displaying modulation metrics Displaying the RDS information in FM Stereo/RDS signals The following topics can be found in this section: Setting Up and Making a Measurement on page 8 Demodulating an AM Signal on page 9 Demodulating an FM Signal on page 11 Demodulating an FM Stereo/RDS Signal on page 13 7
Demodulating AM, FM, ΦM, FM Stereo/RDS Signals Setting Up and Making a Measurement Setting Up and Making a Measurement Making the Initial Signal Connection Set the AM, FM, ΦM, or FM Stereo/RDS transmitter under test to transmit the RF power. Connect the transmitting signal to the signal analyzer as shown below in Figure 1-1. Before connecting a signal to the analyzer, make sure the analyzer can safely accept the signal level provided. The signal level limits are marked next to the RF Input connector on the instrument front panel. 1. Connect the output AM, FM, ΦM, or FM Stereo/RDS transmitter to the RF input port of the signal analyzer using appropriate cables, attenuators, and adapters. 2. (Optional) If there is a frequency reference port on the transmitter, connect it to the EXT REF IN port on the signal analyzer for frequency synchronization. Figure 1-1 AM, FM, ΦM, or FM Stereo/RDS Measurement System After making the connection, see the Input/Output menu for details on selecting input ports and the Amplitude menu for details on setting the internal attenuation to prevent overloading the analyzer. Using Analyzer Mode and Measurement Presets To set your current measurement mode to a known factory default state, press Mode Preset. This initializes the analyzer by returning the mode setup and all of the measurement setups in the mode to the factory default parameters. To preset the parameters that are specific to an active, selected measurement, press Meas Setup, Meas Preset. This returns all the measurement setup parameters to the factory defaults, but only for the currently selected measurement. 8 Keysight N9063C Analog Demod Measurement Guide
Demodulating AM, FM, ΦM, FM Stereo/RDS Signals Demodulating an AM Signal Demodulating an AM Signal This section demonstrates how to demodulate and listen to an AM signal. You can tune to an AM signal and view the results of the detector output displayed in the quad-view window or in single-window format. Alternatively, the demodulated signal is also available as an audio output (to the speaker or headphone jack) and as video output (on the rear panel). The signal under test is a 680 khz signal with AM depth of 50% and AM rate of 1 khz. Note that if you are using a broadcast AM signal in the United States, for example, the AM channels are broadcasting between 550 khz and 1650 khz. Step Action Notes 1. Select Analog Demod mode. Press Mode/Meas, Analog Demod, OK. The default settings for Analog Demod Mode are the AM measurement and Quad View 2. Preset the mode. Press Mode Preset. 3. Set the center frequency of the AM signal. 4. Adjust the sweep time and view the measurement results as in the figure below. Press Center Freq and enter 680, khz. Press Sweep. Press Demod Wfm Sweep Time and enter 2 ms. This is the default setting. Keysight N9063C Analog Demod Measurement Guide 9
Demodulating AM, FM, ΦM, FM Stereo/RDS Signals Demodulating an AM Signal Step Action Notes 5. Listen to the demodulated AM signal. Press Meas Setup, Ad vanced Tab Toggle Demod to Speaker to On You may need to adjust the volume as necessary. 10 Keysight N9063C Analog Demod Measurement Guide
Demodulating AM, FM, ΦM, FM Stereo/RDS Signals Demodulating an FM Signal Demodulating an FM Signal This section demonstrates how to demodulate and listen to an FM signal. You can tune to an FM signal and view the results of the detector output displayed in the quad-view window or single-window format. Alternatively, the demodulated signal is also available as an audio output (to the speaker or headphone jack) and as video output (on the rear panel). The signal under test is a signal at 300 MHz with FM deviation of 10 khz and FM rate of 1 khz. Note that if you are using a broadcast FM signal in the United States, for example, the FM channels are broadcasting between 87.7 MHz and 107.7 MHz. Step Action Notes 1. Select Analog Demod mode. Press Mode/ Meas, Analog Demod. 2. Preset the mode. Press Mode Preset. 3. Select FM measurement. Press Mode/ Meas, FM, OK. The Quad view is the default setting. 4. Set the center frequency to the center of the FM signal. 5. Adjust the sweep time and view the measurement result as in the figure below. Tap Center Freq and enter 300, MHz. Press Sweep, Demod Wfm Sweep Time, 2, ms. This is the default setting. Keysight N9063C Analog Demod Measurement Guide 11
Demodulating AM, FM, ΦM, FM Stereo/RDS Signals Demodulating an FM Signal Step Action Notes 6. Listen to the demodulated FM signal. Press Meas Setup, Ad vanced Tab Toggle Demod to Speaker to On You may need to adjust the volume as necessary. 12 Keysight N9063C Analog Demod Measurement Guide
Demodulating AM, FM, ΦM, FM Stereo/RDS Signals Demodulating an FM Stereo/RDS Signal Demodulating an FM Stereo/RDS Signal This section demonstrates how to demodulate and listen to an FM Stereo signal and view key messages carried in RDS (Radio Data System). You can tune to an FM Stereo/RDS signal and view the measurement results of the multiplexed signal, the mono signal, the stereo signal, the left and right channel of the stereo signal, and the RDS messages in separate views. Alternatively, the demodulated FM Stereo signal is also available as an audio output (to the speaker or headphone jack). Measurement procedures for two typical FM Stereo/RDS signals are introduced here: Measuring L Only FM Stereo/RDS Signals on page 13 Measuring L=R FM Stereo/RDS Signals on page 19 Measuring L Only FM Stereo/RDS Signals The parameters of the signal under test are: FM reference deviation: 75 khz Pilot deviation: 10% Pilot frequency: 19 khz Stereo frequency: 38 khz Left only tone: RDS deviation: 6% 1.0 khz RDS frequency: 57 khz Step Action Notes 1. Select Analog Demod mode Press Mode/Meas, Analog Demod. 2. Preset the mode. Press Mode Preset. 3. Select FM Stereo/RDS measurement. 4. Set the center frequency to the center of the signal and set the AF stop frequency. 5. Set the FM reference deviation. Press Mode/Meas, FM Stereo/RDS. Press FREQ Channel, Center Freq, 98, MHz. Press AF Stop Freq, 65, khz. Press Meas Setup, Ad vanced, Ref Deviation, 75, khz. AF start frequency and AF stop frequency settings determine the span of the X axis in AF Spectrum window in MPX, Mono, Stereo, Left, and Right views. Keysight N9063C Analog Demod Measurement Guide 13
Demodulating AM, FM, ΦM, FM Stereo/RDS Signals Demodulating an FM Stereo/RDS Signal Step Action Notes 6. View the measurement result of the multiplexed signal. Press Display, View, MPX. To display only the current trace in the Demod Waveform window, press Meas Setup and toggle Averaging to Off. The figure below shows the measurement results of the multiplexed signal, including the mono part, stereo part, RDS/RBDS, and pilots. There are four windows: RF Spectrum window (top left) displays the RF spectrum of the multiplexed signal. Demod Waveform window (top right) displays the baseband modulating signal in time domain. There are four traces in this window: maximum trace (in cyan), minimum trace (in magenta), average trace (in green), and current trace (in yellow). AF Spectrum window (bottom left) displays the modulating signal in frequency domain. Metric window (bottom right) displays the numeric measurement results. 7. View the mono part of the multiplexed signal which corresponds to L+R. Press Display, View, Mono. 14 Keysight N9063C Analog Demod Measurement Guide
Demodulating AM, FM, ΦM, FM Stereo/RDS Signals Demodulating an FM Stereo/RDS Signal Step Action Notes 8. View the stereo part of the multiplexed signal which corresponds to L-R. Press Display, View, Stereo. Keysight N9063C Analog Demod Measurement Guide 15
Demodulating AM, FM, ΦM, FM Stereo/RDS Signals Demodulating an FM Stereo/RDS Signal Step Action Notes 9. (Optional) Set the baseband filters to improve the measurement results. 10. If pre-emphasis is used in the signal under test, set to use de-emphasis in the signal analyzer. 11. View measurement results of the left channel. Press Meas Setup, Filters. The highpass filter, lowpass filter, and bandpass filter can be combined as you like. Press Meas Setup, Filters, De-Emphasis and choose the appropriate de-emphasis filter. Press Display, View, Left. 12. View measurement results of the right channel. Press Display, View, Right. The audio in the test signal is an L-only tone, so in the results of the right channel, the demod waveform is almost zero. 16 Keysight N9063C Analog Demod Measurement Guide
Demodulating AM, FM, ΦM, FM Stereo/RDS Signals Demodulating an FM Stereo/RDS Signal Step Action Notes 13. View the RDS/RBDS results. Press Display, View, RDS/RBDS. The figure below displays the BLER result and the information bits in the upper part and key RDS messages like basic tuning and switch information, radio text, and so on in the lower part. For more information, refer to Basic Structure of RDS on page 31 and BLER on page 31. Keysight N9063C Analog Demod Measurement Guide 17
Demodulating AM, FM, ΦM, FM Stereo/RDS Signals Demodulating an FM Stereo/RDS Signal Step Action Notes 14. View a summary of the numeric measurement results. Press Display, View, Results Summary. In this view, the left to right separation result is displayed as "Left to Right" and the mono to stereo crosstalk is displayed as "Mono to Stereo". Normally, the left to right separation test is taken when the audio signal under test is L only or R only; mono to stereo crosstalk test is taken when the audio signal under test is L=R or L=-R. 15. Listen to the demodulated FM stereo signal. Press Meas Setup, Ad vanced Tab Toggle Demod to Speaker to On You may need to adjust the volume as necessary. 18 Keysight N9063C Analog Demod Measurement Guide
Demodulating AM, FM, ΦM, FM Stereo/RDS Signals Demodulating an FM Stereo/RDS Signal Measuring L=R FM Stereo/RDS Signals The parameters of the signal under test are as below. FM reference deviation: 75 khz Pilot deviation: 10% Pilot frequency: 19 khz Stereo frequency: 38 khz Left = Right tone: 1.0 khz RDS deviation: 6% RDS frequency: 57 khz Step Action Notes 1. Select Analog Demod mode. Press Mode, Analog Demod. 2. Preset the mode. Press Mode Preset. 3. Select FM Stereo/RDS measurement. 4. Set the center frequency to the center of the signal and set the AF stop frequency. 5. Set the FM reference deviation. Press Mode/Meas, FM Stereo/RDS. Press FREQ, Center Freq, 98, MHz. Press AF Stop Freq, 65, khz. Press Meas Setup, Ad vanced, Ref Deviation, 75, khz. AF start frequency and AF stop frequency settings determine the span of the X axis in AF Spectrum window in MPX, Mono, Stereo, Left, and Right views. 6. View the measurement result of the multiplexed signal. Press Display, View, MPX. To display only the current trace in the Demod Waveform window, press Meas Setup and toggle Averaging to Off. Keysight N9063C Analog Demod Measurement Guide 19
Demodulating AM, FM, ΦM, FM Stereo/RDS Signals Demodulating an FM Stereo/RDS Signal Step Action Notes The figure below shows measurement results of the multiplexed signal, including the mono part, the stereo part, RDS/RBDS, and pilots. There are four windows: RF Spectrum window (top left) displays the RF spectrum of the multiplexed signal. Demod Waveform window (top right) displays the baseband modulating signal in time domain. There are four traces in this window: maximum trace (in cyan), minimum trace (in magenta), average trace (in green), and current trace (in yellow). AF Spectrum window (bottom left) displays the modulating signal in the frequency domain. Metric window (bottom right) displays the numeric measurement results. 7. View the mono part of the multiplexed signal which corresponds to L+R. Press Display, View, Mono. 20 Keysight N9063C Analog Demod Measurement Guide
Demodulating AM, FM, ΦM, FM Stereo/RDS Signals Demodulating an FM Stereo/RDS Signal Step Action Notes 8. View the stereo part of the multiplexed signal which corresponds to L- R. Press View/Display, Stereo. Keysight N9063C Analog Demod Measurement Guide 21
Demodulating AM, FM, ΦM, FM Stereo/RDS Signals Demodulating an FM Stereo/RDS Signal Step Action Notes 9. (Optional) Set the baseband filters to improve the measurement results. 10. If pre-emphasis is used in the signal under test, set to use de-emphasis in the signal analyzer. 11. View the measurement results of the left channel. Press Meas Setup, Filters. The highpass filter, lowpass filter, and bandpass filter can be combined as you like. Press Meas Setup, Filters, De-Emphasis and choose the appropriate de-emphasis filter. Press Display, View, Left. In this test case, the left channel equals to the right channel. 12. View the RDS/RBDS results. Press Display, View, RDS/RBDS. 22 Keysight N9063C Analog Demod Measurement Guide
Demodulating AM, FM, ΦM, FM Stereo/RDS Signals Demodulating an FM Stereo/RDS Signal Step Action Notes The figure below displays the BLER result and the information bits in the upper part and key RDS messages like basic tuning and switch information, radio text, and so on in the lower part. For more information, refer to Basic Structure of RDS on page 31 and BLER on page 31. 13. View a summary of the numeric measurement results. Press Display, View, Result Summary. Keysight N9063C Analog Demod Measurement Guide 23
Demodulating AM, FM, ΦM, FM Stereo/RDS Signals Demodulating an FM Stereo/RDS Signal Step Action Notes In this view, the left to right separation result is displayed as "Left to Right" and the mono to stereo crosstalk is displayed as "Mono to Stereo". Normally, the left to right separation test is taken when the audio signal under test is L only or R only; mono to stereo crosstalk test is taken when the audio signal under test is L=R or L=-R. 14. Listen to the demodulated FM stereo signal. Press Meas Setup, Ad vanced Tab Toggle Demod to Speaker to On You may need to adjust the volume as necessary. 24 Keysight N9063C Analog Demod Measurement Guide
Keysight X-Series Signal Analyzer N9063C Analog Demod Measurement Application Measurement Guide 2 Concepts The following topics can be found in this section: AM Concepts on page 26 FM Concepts on page 28 FM Stereo/RDS Concepts on page 30 Modulation Distortion Measurement Concepts on page 32 Modulation SINAD Measurement Concepts on page 33 25
Concepts AM Concepts AM Concepts Figure 2-1 AM waveform In AM (Amplitude Modulation), the instantaneous amplitude of the modulated carrier signal changes in proportion to the instantaneous amplitude of the information signal. Figure 2-2 Calculation AM index in time and frequency domain The modulation index "m" represents the amount of modulation or the degree to which the information signal modulates the carrier signal. The index for an AM signal can be calculated from the amplitudes of the carrier and either of the sidebands by the equation: Equation 2-1 m = E ----------------- max E c = Emax --------------------- E min = E USB + E --------------------- LSB = 2E SB -------- + E c E max E min E c E c 26 Keysight N9063C Analog Demod Measurement Guide
Concepts AM Concepts For 100% modulation, the modulation index is 1.0, and the amplitude of each sideband will be one-half of the carrier amplitude expressed in voltage. On a decibel power scale, each sideband will thus be 6 db less than the carrier, or one-fourth the power of the carrier. Since the carrier power does not change with amplitude modulation, the total power in the 100% modulated wave is 50% higher than in the unmodulated carrier. The relationship between m and the logarithmic display can be expressed as: Equation 2-2 ( )db + 6dB = 20logm E SB E c Keysight N9063C Analog Demod Measurement Guide 27
Concepts FM Concepts FM Concepts Figure 2-3 FM waveform FM (Frequency Modulation) and PM (Phase Modulation) belong to angle modulation. In FM, the instantaneous frequency deviation of the modulated carrier signal changes in proportion to the instantaneous amplitude of the modulating signal. And in PM, the instantaneous phase deviation of the modulated carrier with respect to the phase of the unmodulated carrier is directly proportional to the instantaneous amplitude of the modulating signal. The modulation index for angle modulation, β, is expressed by this equation: Equation 2-3 β = Δ f p f m = ΔΦ p Where Δfp is the peak frequency deviation, fm is the frequency of the modulating signal, and Δφp is the peak phase deviation. This expression tells us that the angle modulation index is really a function of phase deviation, even in the FM case. Also, the definitions for frequency and phase modulation do not include the modulating frequency. In each case, the modulated property of the carrier, frequency or phase, deviates in proportion to the instantaneous amplitude of the modulating signal, regardless of the rate at which the amplitude changes. However, the frequency of the modulating signal is important in FM and is included in the expression for the modulating index because it is the ratio of peak frequency deviation to modulation frequency that equates to peak phase. Unlike the modulation index for AM, there is no specific limit to the value of β, since there is no theoretical limit to the phase deviation; thus there is no equivalent of 100% AM. However, in real world systems there are practical limits. 28 Keysight N9063C Analog Demod Measurement Guide
Concepts FM Concepts Unlike AM, which is a linear process, angle modulation is nonlinear. This means that a single sine wave modulating signal, instead of producing only two sidebands, yields an infinite number of sidebands spaced by the modulating frequency. The Bessel function graph shows the amplitudes of the carrier and the sidebands as a function of the modulation index, β. The spectral components, including the carrier, change their amplitudes as the modulation index varies. Figure 2-4 Carrier and sideband amplitude for angle-modulated signals In theory, for distortion-free detection of the modulating signal, all the sidebands must be transmitted. However, in practice, the sideband amplitudes become negligibly small beyond a certain frequency offset from the carrier, so the spectrum of a real-world FM signal is not infinite. Keysight N9063C Analog Demod Measurement Guide 29
Concepts FM Stereo/RDS Concepts FM Stereo/RDS Concepts FM stereo is an enhancement of FM using stereo multiplexing. An FM stereo signal carries stereophonic programs in which different contents are transmitted for L (left) and R (right) audio channels. RDS (Radio Data System) is the text information such as traffic, weather, and radio station information carried in FM signals. This information can be displayed on the screen of the end-user s device. The following figure shows the baseband spectrum of the FM stereo signal including RDS data. Figure 2-5 Baseband spectrum of the FM Stereo/RDS signal FM Stereo RDS/RBDS The FM stereo multiplexed signal consists of a mono (L+R) signal, a stereo (L-R) signal, and a pilot signal. As shown in Figure 2.5, the mono (L+R) signal occupies the lower part of the baseband spectrum (50 Hz ~ 15 khz) to keep backward compatibility with the previously monophonic FM systems. The (L-R) signal is amplitude modulated onto a suppressed subcarrier at 38 khz. A pilot signal is transmitted at 19 khz and is used by the receiver to identify a stereo transmission and reconstruct L and R audio signals from the multiplexed signal. In the receiver, the (L+R) signal is added to the (L-R) signal to get the L signal, and subtracts the (L-R) signal to get the R signal. The standard documents for RDS and RBDS are as follows: IEC 62106: Specification of the radio data system (RDS) for VHF/FM sound broadcasting in the frequency range from 87.5 to 108.0 MHz. EIA/NAB NRSC: United States RBDS standard - Specification of the radio broadcast data system (RBDS). 30 Keysight N9063C Analog Demod Measurement Guide
Concepts FM Stereo/RDS Concepts RBDS is the United States version of RDS. Both RDS and RBDS are intended for application to VHF/FM sound broadcasts in the range 87.5 MHz to 108.0 MHz which may carry either stereophonic or monophonic programs. The main objectives of RDS/RBDS: To enhance functionality for FM receivers; To make the receivers more user-friendly by using features such as PI (program identification), PS (program service) name display, and if applicable, automatic tuning for portable and car radios. As shown in Figure 2-5, RDS/RBDS uses the 57 khz subcarrier to carry the data at 1.1875 kbps bitrate. The 57 khz is chosen to be the third harmonic of the pilot tone. The deviation range of the FM carrier due to the unmodulated RDS/RBDS subcarrier is from ±1.0 khz to ±7.5 khz. Basic Structure of RDS The basic structure of RDS is shown in Figure 2-6, in which the largest element is called a group including 4 blocks of 26 bits each. Each block comprises an information word (16 bits) and a checkword (10 bits). The information word is used to transmit information to the end user. The 10-bit checkword plus offset word are used to provide error protection and block and group synchronization information. Figure 2-6 Basic structure of RDS BLER BLER (block error rate) is the ratio of the number of un-correctable blocks to the total number of blocks received. Normally, BLER should be less than 5%. Keysight N9063C Analog Demod Measurement Guide 31
Concepts Modulation Distortion Measurement Concepts Modulation Distortion Measurement Concepts Purpose This measurement is used to measure the amount of modulation distortion contained in the modulated signal by determining the ratio of harmonic and noise power to fundamental power. This measurement verifies the modulation quality of the signal from the DUT. Measurement Technique Modulation Distortion is defined as: Equation 2-4 P total P signal % ModulationDistortion = --------------------------- 100% P total where: P total = the power of the total signal, P signal = the power of the wanted modulating signal, and P total - P signal = total unwanted signal which includes harmonic distortion and noise. First, the received signal is demodulated and filtered to remove DC. Then the filtered signal is transformed by an FFT into the frequency domain. Next, total power in the total filter band is measured as P total, the peak power of the modulated signal is computed as P signal, the square root of the ratio of P total - P signal to P total is calculated. The result is the signal s modulation distortion. It can be expressed as db or %. 32 Keysight N9063C Analog Demod Measurement Guide
Concepts Modulation SINAD Measurement Concepts Modulation SINAD Measurement Concepts Equation 2-5 Purpose Modulation SINAD (SIgnal to Noise And Distortion) measures the amount of Modulation SINAD contained in the modulated signal by determining the ratio of fundamental power to harmonic and noise power. Modulation SINAD is the reciprocal of the modulation distortion provided by the Modulation Distortion measurement. This is another way to quantify the quality of the modulation process. Measurement Technique Modulation SINAD is defined as: db ModulationSINAD = 20 log P --------------------------- total P total P signal where: P total = the power of the total signal, P signal = the power of the wanted modulating signal, and P total - P signal = the total unwanted signals which include harmonic distortion and noise. First, the received signal is demodulated and filtered to remove DC, then the filtered signal is transformed by an FFT into the frequency domain. Next, total power in the total filter band is measured as P total, the peak power of the modulated signal is computed as P signal, the square root of the ratio of P total to P total - P signal is calculated. The result is the signal s Modulation SINAD. It can be expressed as db. Keysight N9063C Analog Demod Measurement Guide 33
This information is subject to change without notice. Keysight Technologies 2008-2016 Edition 1, February 2016 N9063-90001 www.keysight.com